How to monitor Rifampicin - a brief primer
A number of important considerations are required before prescribing Rifampicin:
- Is a Rifampicin-containing regimen the optimal regimen for the patient’s infection?
- If yes, are the bacteria thought to be causing the infection susceptible to Rifampicin? It has been our policy not to prescribe Rifampicin without susceptibility testing first if the patient is culture positive, although it is possible that any anti-biofilm activity is not susceptibility dependent. We do use Rifampicin for culture negative infections on occasions, however, providing there is a high probability the presumed causal bacteria are likely to be susceptible and the benefits outweigh the risks.
Does the patient have any underlying medical conditions, particularly hepatic, that might change the risk/benefit ratio of using Rifampicin?
Is the patient taking any other medications that are high risk for hepatic adverse effects and might change the risk/benefit ratio of using Rifampicin?
Does the amount of alcohol the patient drinks change the risk/benefit ratio of using Rifampicin?
Does the patient use contact lenses? (potential for discolouration)
Weight of patient – we generally use 450mg twice daily for patients of 60kg or more and 300mg twice daily for those who are less than 60kg.
- Have pre-treatment bloods (full blood count and renal/hepatic bloods) been checked?
- We always check bloods at baseline and then at two and six weeks after starting and eight weekly thereafter as a minimum. In patients with, for example, hepatic disease, when use is felt to be essential, a more frequent monitoring regimen is appropriate (e.g. weeks 1, 2, 4 and 6 after commencement and then monthly).
- Patient medication list – Rifampicin has too many drug-drug interactions, that mainly decrease the patient’s exposure to the other drug, to review here, but as with all antibiotics, the potential for drug-drug interactions should be checked using a reliable resource such as the British National Formulary specifically for Rifampicin.
We rarely prescribe Rifampicin for a patient prescribed Warfarin as in our experience it can be very challenging to maintain a therapeutic international normalised ratio (INR), although on occasions Rifampicin-based therapy is mandated.
Rifampicin also decreases exposure to some potential partner antibiotics (Chloramphenicol, Clarithromycin, Doxycycline, Linezolid and Trimethoprim), but the clinical importance of this is unclear, although the Doxycycline-Rifampicin interaction has been shown to negatively impact outcome in Brucellosis (please find resources in the see also section below).
In general, we avoid such combinations, although we do have extensive experience of successfully using Doxycycline plus Rifampicin for a variety of bone and joint infections; we usually increase the dose of Doxycycline to 150mg twice daily to account for this potential interaction.
One important, albeit harmless, adverse effect of Rifampicin, that patients should be made aware of, is the potential for it to cause red/orange coloration of secretions and bodily fluids (tears, saliva and urine), although not all patients experience or notice this.
Otherwise, the most common adverse effects that we experience in our COPAT service are gastrointestinal. For nausea and vomiting, dose reduction (from 450mg to 300mg twice daily) can help and/or the use of an anti-emetic 30 to 45 minutes pre-dose, although in some cases symptoms are intractable despite these measures. We also find probiotics helpful for some (but certainly not all) patients with lower gastrointestinal disturbance (Note: probiotics should be avoided in notably immunocompromised patients); see resources in the see also section below.